The present invention relates to controls for independently adjusting the temperatures in the freezer and fresh food compartments in a refrigerator having an evaporator in the freezer compartment and an evaporator in the fresh food compartment.
The presently used refrigeration cycle in household refrigerators is the simple vapor compression type using a single evaporator. Relative cooling rates for the freezer and the fresh food compartments are controlled by the user. A user adjusted control, sets the fixed fraction of the total cold air flow provided by the single evaporator and fan which is to reach the two refrigerator compartments. When the temperature of the fresh food compartment rises above a preset level, the compressor operates allowing the evaporator to supply cold air. Since the fraction of cold air provided to the fresh food and freezer compartments does not vary once set, control of freezer temperature is imperfect and freezer air temperatures vary considerably. Changes in the ambient temperature, time defrosts of the freezer compartment, and changes of incidental thermal loads (door opening frequency and duration) requires time varying changes in the fraction of cold air delivered to both compartments to properly control the temperature in both compartments.
In a refrigeration cycle having dual evaporators such as the one shown in U.S. Pat. No. 4,910,972, hereby incorporated by reference, distinct cooling rates are provided by each evaporator during steady state operation. One evaporator operates at a temperature of approximately -10.degree. F. and the other at approximately 25.degree. F. to provide cold air to the freezer and fresh food compartments, respectively. The cooling rates of the two evaporators depend entirely on heat exchanger and compressor designs, choice of refrigerant, ambient temperature, refrigerator cabinet thermal conductance and thermal loads other than conduction to the ambient. To provide separate and distinct narrow temperature ranges of operation in each of a refrigerators two compartments, provisions must be made to adjust the relative cooling rates of the two evaporators in response to changing ambient temperatures and incidental thermal loads.
It is an object of the present invention to provide a control for regulating the cooling rates of a refrigerator equipped with a dual evaporator refrigerator system.